Furnace apparatus for the treatment of raw materials



March 8, 1966 E. MAIER ETAL 3,239,593

FURNACE APPARATUS FOR THE TREATMENT OF RAW MATERIALS I Original FiledJan. 9, 1961 2 Sheets-Sheet l March 8, 1966 E. MAIER ETAL FURNACEAPPARATUS FOR THE TREATMENT OF RAW MATERIALS 2 Sheets-Sheet 2 OriginalFiled Jan. 9, 1961 United States Patent f 3,239,593 FURNACE APPARATUSFOR THE TREATMENT OF RAW MATERIALS Erwin Maier, Gotthart Michael Maier,and Johann Imannel Maier, all of Laufenburg, Baden, Germany, assignorsto Oxymet Ag, Baden, Switzerland Original application Jan. 9, 1961, Ser.No. 81,620, now Patent No. 3,180,915, dated Apr. 27, 1965. Divided andthis application Jan. 12, 1965, Ser. No. 424,903 Claims priority,application Switzerland, Jan. 12, 1960, 273/60 Claims. (Cl. 13-9) Thisapplication is a division of application Serial No. 81,620, filedJanuary 9, 1961, now Patent No. 3,180,915.

The present invention relates to a quickly rotating electric arc furnaceand to a method for its operation.

It is a principal object of the present invention to provide a rotaryelectric arc furnace capable of being operated at high voltages and lowcurrent intensities.

It is another object of the invention to provide a rotary electric arcfurnace the interior of which, and the electrodes arranged therein, areeasily accessible for inspection, repair or replacement, respectively.

It is yet another object of the invention to provide apparatus foroperating a rotary electric arc furnace wherein raw materials can betreated which initially are poorly electrically conductive or not at allconductive.

With these and other objects in view which will become apparent laterfrom this specification and the accompanying drawings, apparatus isprovided for the treatment of raw materials which initially aresubstantially non-conductive, comprising the steps of quickly rotating ahollow furnace, applying said raw material to the inner wall surface ofsaid furnace as a surface layer, making said material adhere as asurface layer to said surface by centrifugal force, applying an igniterlayer of selected width to the said surface layer, applying at least oneelectric arc to said igniter layer, forming an annular reaction groovein said surface layer under said igniter layer, and confining thereactions in said furnace to said groove.

The igniter layer may consist of an exothermic, for examplealuminothermic, selfheating material, or it may be formed out of thefree surface of the layer of raw material by reacting it with anauxiliary flame impinging on it and, for example, superficiallyconverting the same into slag.

The width of the reaction groove may be controlled electrically byvarying the diameter of the electrodes or the distance thereof from thegroove. By placing several electrodes at different but adjacent levelsthe width of said reaction groove may for example be increased.

The shape and size of said groove may be alternatively or additionallycontrolled mechanically by the way in which at least part of the rawmaterial to be treated is supplied to the reaction groove.

The furnace according to the invention comprises in combination: astationary shell and two truncated cones journalled co-axially to oneanother and to the stationary shell and with annular interspacing fromone another, drive means in operation driving the cones at differed tialrotational speeds, feeder means supplying raw material to be treatedinto the annular interspaced between the two cones, and a materialsreceiving chamber in the bottom of the furnace.

Preferably this furnace has a nonrotatable bottom and a system ofelectrodes insulated from and mounted on such bottom with their freeends in juxtaposition with the inner surface of the outer one of the twotruncated cones, and with the bottom and electrode system forming aself-contained unit axially movable relative to the rest of the furnace.

Patented Mar. 8, 1966 These and other features of this invention will beclearly understood from the following description of a preferredembodiment thereof given with reference to the accompanying drawings, inwhich:

FIG. 1 is a vertical longitudinal section of a rotary electric furnace;

FIG. 2 is a cross section on the line lI-II of FIG. 1, as seen in thedirection of the arrow, some details being omitted;

FIG. 3 is a detail of FIG. 1 on a larger scale, namely the bottomportion of the furnace;

FIG. 4 is a view of the bottom portion in the direction of the arrowsIV-IV of FIG. 3; and

FIG. 5 is a diagrammatic detail of the reaction groove and itsvariation.

As is illustrated in FIG. 1, the rotary electric furnace embodying thepresent invention includes A casing consisting of a steel sheet shell 1,carried by three or four pillars 2. On top the casing is covered by acover 3 having a cylindrical socket 4.

In the casing a cone 5 of steel sheet is rotatable, the tyre 6 of whichis carried and driven by, for example, three driving rollers 53, each ofwhich is mounted on the output shaft of a motor 7. These motors 7 arefixed to the outside of the casing 1. The steel sheet cone 5 iscontinued downwardly by another cone 8 and a short cylindrical portionhaving a tyre 9, thence terminating in an opposite cone 10. The tyre 9is centered and guided by means of, for example, three rollers 11, whichare substantially sheltered from the actions of the furnace and aremounted, in order to be accessible from outside, in capsules 54 on thecasing 1. Inside the cone 5 rotates another cone 25 of smaller diameter,however at a differential velocity with respect to the outer cone 5, inorder that the material 55 fed by a helix 14 to helical threads 26arranged on cone 25 may advance downwardly into the inner space of thefurnace, against a pyroplastic phase which may form and which cannot beovercome by the mere action of centrifugal and thrust force, asexperience has shown.

On top of the inner cone 25 is a cylindrical extension 27 withrefractory brick lining 28 on its inside wall serving as a chimney stackfor the furnace; on its outside wall there is a labyrinth gland 29 and aset of slip rings 30 for the electricity supply. The inner cone 25 isheld by a carrier steel plate 31, as is shown in FIG. 1 wherein theupwardly extending part of the frustro-conical shape of cone 25 isconnected to the plate 31 by arms 13. The plate 31 is supported by meansof a flange 32 on the driving ring 6. The par-ts 25, 13 and 31 aredriven at a speed higher or lower than that of the outer cone 5,depending on whether it is a clockwise or anti-clockwise rotation, by ageared electric motor 33 connected to the slip rings 30.

The material 55 to be treated is fed by the helix 14 .and drips into theinterspace 12 between the conical sheet metal shells defining the wallsof outer and inner cones 5 and 25 which are internally lined with firebricks 28. To this introduced material 55 a downward thrust is appliedby the action of gravity and of centrifugal force. At the same time itforms a coating of insulating material with respect to the annularreaction groove 16 forming opposite the electrodes 18. The materialtreated in this reaction groove 16 is fused; such liquid material isaccordingly forced out of the reaction groove 16 and sinks down to theedge 17 of the shell from where it is sprayed off to the outer casingwall 1. Electric energy is transmitted to the reaction groove 16 by thearcs of three or six electrodes 18. These electrodes 18 are insertedfrom below into the interior of the furnace casing 1, by means ofelectrode holders 19 which are insulated from and mounted on a bottom29. This bottom 20 is in turn capable of being lowered together with theelectrode holders 19 and electrodes 18 by means of three hoist spindles21, in order to be able to exchange the graphite electrodes or to repairany damage in the interior of the furnace, when necessary. In the bottom20, in addition to the electrode holders, a longitudinally slidable tube34 is attached for spraying a substance, for such as an igniter layer origniter flame on the surface of the reaction groove 16. The feed of theelectrodes is effected by a geared motor 35 cooperating with a threadedspindle 59 of the electrode holder 19 (FIG. 2). A further geared motor36 in the casing 58 serves for driving a toothed crown 23 for a scraper.The hoist spindels 21 are driven in unison by the gearing 38 arranged onthe hoist stocks 37, for example by two geared motors 39 in order thatno jamming may occur when raising or lowering an electrode-carryingbottom 20.

As is illustrated in FIG. 2, the dome shaped bottom 20 is lowered bymeans of the two motors 39 which operate the gearing 38 and the hoiststocks 37 to cause vertical movement of the threaded spindles 21. Withsuch an arrangement, a simple operation permits the whole interior ofthe furnace to be accessible for dismantling and repair.

The sprayed off reaction material 57, for example metal, is cooled onthe wall of the furnace casing 1 and then drops in granulated form intothe collector trough 22 whence it is conveyed by a toothed scraper crown23 to the trough 58 of a helix, and is finally discharged by the helix24 therein for further use.

In FIG. 3 the enlargement of the reaction groove 16 by the arrangementof pivotal electrode holders 19 is illustrated. These holders 19 areprovided each with a collar 60 comprising a worm wheel segment 61 inmesh with a worm 40 which can be turned by a spindle 62 and a hand wheel41, to the left or to the right, as desired. In FIGS. 3 and 4 the effectof this adjustment is illustrated in dotted lines as well as thevariation in the shape of the reaction groove 16 caused thereby. Inparticular, the hatching in FIG. 3 shows that by pivoting the electrodesdownward or by inserting thicker electrodes the reaction groove travelsto a lower place in the furnace.

FIG. 4 shows in dotted lines a position of the electrodes lying closerto the reaction groove 16 than in the position shown in full lines. Theresult of this approach according to FIG. 4 is the formation of a deeperbut narrower groove 16, corresponding approximately to the hatchedprofile in FIG. 3.

In FIG. part of the reaction groove 16 corresponding to that of FIGS. 1and 3 is illustrated. It will be seen, how by the increased feed ofmaterial 55 in the direction of the arrow, the groove is made tobulge-in from above, and the conductive area is reduced. Feed of thefresh material 55 in the direction of the arrow 63 will make the groove16 narrower; when underpinning the groove 16 with fresh material 55 inthe direction of the arrow 64 the groove is made more shallow.

It is a characteristic of the method described that the reaction groove16 may be placed on any point of the furnace desired. This groove 16,although situated within the material to be treated, behaves physicallyand technologically quite differently from it. The layer of the material55 forms structurally so to stay within the furnace treatment chamberadjacent the groove 16. This difference in behavior applies also to thedischarge of the finally treated matter from the groove 16, providedthis matter is liquid. This liquid 56 flows over the material to betreated 55 or seeps through it under the action of gravity and ofcentrifugal force, and flows towards the spraying-off edge 1'7 as ifboth were different materials, and without reacting with it, firmlyadhering to it, or forming slag. In a regular run of the furnace theliquid (metal) is continuously thrown off from the edge 17 and likewisecontinuously flows from the groove 16.

Once the reaction groove 16 has been formed, it remains in existencethroughout the whole of the further operation of the furnace, even whennew material is fed into this groove for treatment from its margins orfrom the surface.

The extraordinary advantage and the considerable simplicity of themethod described consist in that owing to the formation of thisaccurately defined groove the working process of the furnace takes placeonly therein, and that accordingly finished reactive matter can becontained only in it. This matter may be liquid, and in this case it canbe very easily withdrawn from this sharply localized zone and out of thefurnace. However, the matter may alternatively be vaporised or gasifiedwithin this reaction groove.

In any case the extent of the treatment finally carried out in thisgroove can be accurately supervised and controlled, and accordingly therequired replenishing of the groove can be at least estimated.

On the basis of experience, the profile and length of the reactiongroove development can be determined for any individual case ofoperation and for any material to be treated. From such data, the natureof the material and the temperature gradient, the electrical resistancein operation is determined. The same depends on the length of the pathof current and on the width of the band of current, apart from theelectrical constants of the material to be treated, e.g., the variationof conductivity of the actual raw material with the variations intemperature. The width of the groove in turn depends, in a quitedefinite manner to be ascertained by tests, on the size of theelectrodes, their angular position relative to the material andaccordingly on the kind of electric are forming, and to a less extentalso on the width of the igniter layer.

The economic advantage always aimed at in the operation of electricfurnaces for carrying out metallurgical and other processes is to beable to operate at high voltages and low current intensities, which isattained by the method described. The most favourable data for suchvoltages and current can even be calculated in advance; during operationthey can moreover be regulated in the manner desired, since the voltagesgenerated are determined in the first place by the profile of thereaction groove, and this profile is controlled during operation withinwide limits.

In the method described for the operation of the furnace the followingmeans, inter alia, are readily available for controlling the voltagesand intensities of the current:

(a) The thickness and depth, respectively of the reaction groove isinfluenced mechanically in the simplest manner by the supply of newmaterial to be treated from one side or from both sides or even from theground below the reaction layer (underspinning). Its width can bemechanically reduced by an increased supply of new material to betreated from the surface of the groove. Moreover the width of theigniter layer applied to be material to be treated for initiating theWorking process has an effect on the formation of the surface width ofthe reaction groove.

(b) The width of the groove surface can moreover be influencedelectrically by the distance of the electrodes from the surface of thelayer to be treated; moreover by the angular position of the electrodesrelative to the surface of the reaction groove, by the magnitude of thediameter of the electrodes and additionally in that the differentelectrodes acting on the reaction groove are not placed in the sameplane.

The possibilities of influencing the groove according to (a) and (b) areindependent of one another to a great extent. They supplement oneanother in accordance with the operation chosen.

Within the groove the reacted material is always more movable,particularly relative to the rest of the material fed into it and to thefurnace containing the groove. The groove may contain the matter in theliquid phase or in finely divided solid form which gradually forms abulge on the surface of the groove. The liquid phase or the bulge of thefinally treated material may be scraped off from the groove, e.g., bymeans of conventional mechanical means. With regard to the materialcontained in the groove in the vapour or gaseous phase, it will escapetherefrom by itself. In this case a cavity is formed within the flow ofthe material, as viewed from the form of the furnace.

The igniter layer may be composed of exothermic e.g. aluminothermicheating substances which are applied during rotation of the furnace onthe form of a ring onto the layer of raw material; the arcs of theelectrodes act on this igniter layer in such a manner that below theigniter layer there is formed the reaction groove of molten metal whichis now conductive. The igniter layer may alternatively be formed bysuperficially reacting the raw material (slag formation) by means of aheating flame.

While we have described herein and illustrated in the accompanyingdrawings what may be considered a typical and particularly usefulembodiment of our invention, We wish it to be understood, that we do notlimit ourselves to the particular details and dimensions described orillustrated inasmuch as obvious modifications will occur to a personskilled in the art.

What is claimed is:

1. A furnace for the treatment of raw materials which initially areelectrically substantially non-conductive comprising in combination: astationary shell and two truncated cones journalled c-o-axially to oneanother and to said stationary shell and with annular interspacing fromone another, drive means in operation driving the said cones atdifferent rotational speeds, feeder means supplying raw materials to betreated into the annular interspacing between the said two cones,furnace bottom means disposed beneath said cones, and a materialsreceiving chamber defined by the outer one of said cones and saidfurnace bottom means.

2. A furnace as claimed in claim 1 comprising a furnace stack integralwith the inner one of the said two truncated cones.

3. A furnace as claimed in claim 1 wherein said furnace bottom meanscomprises a bottom adjustable to a set position and a system ofelectrodes mounted insulated from said bottom, said electrodes havingfree ends in juxtaposition to the inner surface of the outer one of saidtwo cones, said bottom and electrodes forming a selfcontained unitaxially movable relative to the rest of the said furnace, and means foraxially moving said bottom for adjustment to a set position.

4. A furnace as claimed in claim 3 wherein the said bottom is a domeshaped body and is symmetrical to the axis of the said furnace.

5. A furnace as claimed in claim 3, comprising an annular trough for thefinished product attached to the said bottom and surrounding the same.

References Cited by the Examiner UNITED STATES PATENTS 1,496,232 6/1924Klugh 1333 1,751,335 3/1930 Kennedy 214-35 X 1,891,821 12/1932 Juengling21437 RICHARD M. WOOD, Primary Examiner.

JOSEPH V. TRUHE, SR., Examiner.

1. A FURNACE FOR THE TREATMENT OF RAW MATERIALS WHICH INITIALLY AREELECTRICALLY SUBSTANTIALLY NON-CONDUCTIVE COMPRISING IN COMBINATION; ASTATIONAY SHELL AND TWO TRUNCATED CONES JOURNALLED CO-AXIALLY TO ONEANOTHER AND TO SAID STATIONARY SHELL AND WITH ANNULAR INTERSPACING FROMONE ANOTHER, DRIVE MEANS IN OPERATION DRIVING THE SAID CONES ATDIFFERENT ROTATIONAL SPEEDS, FEEDER MEANS SUPPLYING RAW MATERIALS TO BETREATED INTO THE ANNULAR INTERSPACING BETWEEN THE SAID TWO CONS, FURNACEBOTTOM MEANS